Adds a new frontend option
"-experimental-allow-module-with-compiler-errors". If any compilation
errors occur while generating the .swiftmodule, this mode will skip SIL
entirely and only serialize the (likey invalid) AST.
This existence of this option during generation is serialized into the
resulting .swiftmodule. Errors found in deserialization are only allowed
if it is set.
Primarily intended for IDE requests (eg. indexing and code completion)
to ensure robust cross-module results, despite possible errors.
Resolves rdar://69815975
Otherwise, hits assertion, or crashes in no-assertion build.
Added 'EditableTextBuffer::getSize()' for getting size after previous updates
without actually applying them.
rdar://problem/34206143
This provides a very rudimentary way to check the end-to-end performance
of simple sourcekitd requests. A sample invocation might be
```
sourcekitd-test -time-request -repeat-request=10 -dont-print-response -req= ...
```
